It is known for passenger aircraft to include ‘at-seat’ passenger entertainment systems, with a passenger entertainment station being provided for each passenger, installed in or adjacent to each passenger's seat. Such systems allow passengers to insert a plug of a headphone set (or indeed other sound reproduction equipment) into an audio socket of the station and then listen to audio content provided by the system. Such systems typically allow each passenger to select one of a number of channels, for example including music or the spoken word, in conjunction with, or independently of, displayed visual content. During changeover periods between passengers leaving the aircraft and prior to new passengers boarding the aircraft, aircraft crew need to ensure that each passenger entertainment station is functioning correctly (prior to arrival of the new passengers). This check may include inserting the plug of a headphone set into the socket, or jack, of each station and verifying that there is audible content. We have realised that this procedure could be made more efficient by providing an improved passenger entertainment system.